The present invention pertains to power monitors and particularly to laser source power monitors.
Vertical cavity surface emitting lasers in fiber optic communications require a feedback circuit so that the output power of the laser in the on-state can be maintained at a constant level during ambient temperature changes or the aging of the device incorporating the laser. In order to monitor the output power of the laser, some fraction of the output of the laser must be directed to a sensing device such as a photo detector. The output of this photo detector or sensing device is sent to a control circuit which adjusts the current driving the laser until the desired output power is achieved. For a vertical cavity surface emitting laser, a beam splitter may be placed at the output of the laser, which would direct some of the light to a photo detector, permitting the rest of the light to be directed into the optic fiber. However, this approach reduces the amount of light which can be coupled into the optic fiber. This reduction of light being coupled into the optic fiber affects the power margin or requires that the output of the laser and the associated power dissipation be higher than it would otherwise need to be. This power monitoring approach increases packaging complexity of such laser source.